The invention is in the field of photoflash lamps of the electrically fired type and designed to provide a short circuit, or relatively low impedance, across its lead-in wires after the lamp has been flashed.
U.S. Pat. No. 3,532,931 to Paul Cote and John Harnden shows, in FIGS. 1 and 2, a type of flash lamp sequencing circuit utilizing switches that are normally open (or high impedence) and which close (or change to low impedance) upon flashing of the lamps, and the lamps must have open circuits (or high impedance) across their lead-in wires after flashing. FIG. 3 of the same patent shows a different type of flash lamp sequencing circuit, in which switches (such as fuses) initially have a low impedance and become open-circuited (or high impedance) upon flashing of the lamps, and the lamps must become electrically shorted (or have a low impedance) across their lead-in wires upon flashing. The same patent describes the alternatives of employing lamps in the FIG. 3 circuit which reliably short upon flashing, and/or connecting switch devices across the lamps to achieve the same result in the sequencing circuit. U.S. Pat. No. 3,692,995 to Karl Wagner also shows a flash lamp sequencing circuit which employs openings switches and shorting lamps, and describes a type of shorting lamp in which the electrodes melt together. The above-referenced patent application discloses a shorting lamp construction having a primer material, between the lead-in wires in the lamp, which ignites combustible material in the lamp in response to a firing voltage pulse, and the primer material thereupon forms a conductive residue which provides a short circuit, or relatively low impedance, across the lead-in wires.
The lamps described above can be the so-called high voltage type of lamp which can be fired by a low energy voltage pulse of about 100 volts or more, and frequently in the range of about 1000 to 3000 volts such as can be produced by impacting a piezoelectric element. U.S. Pat. Nos. 2,972,937 and 3,106,080 to C. G. Suits disclose a high voltage flash lamp and a piezoelectric firing arrangement.